Characterization of Chemical Composition along the Molar Mass Distribution in Polyolefin Copolymers by GPC Using a Modern Filter-Based IR Detector

Polyolefin Characterization – ICPC 2012. Macromolecular Symposia.
Volume 330, 2013, Pages 63-80,
A. Ortín, J. Montesinos, E. López, P. del Hierro, B. Monrabal, J.R. Torres-Lapasió, M.C. García-Álvarez-Coque.
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Abstract:

Gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), is the technique routinely used at high temperature to analyze the molar mass distribution in polyolefins. The distribution of comonomer along the molar mass distribution in a copolymer is a key microstructural feature that determines the macroscopic properties of the material, and thus, its range of possible applications and performance. The direct coupling of a modern filter-based infrared (IR) detector to a high-temperature GPC instrument, by means of a heated flow-through cell, is here described. The analyses are carried out by recording the continuous IR absorbance chromatograms at selected bands, which show different sensitivities to the different monomer units. A slice-by-slice ratio of the IR bands is further calculated to determine the average chemical composition of each molar mass fraction, after GPC separation. The high sensitivity of this IR detection method allows the injection of low concentrations of sample and the use of standard GPC analysis conditions so that chromatographic quality is not compromised even in cases where very high molar mass fractions are present. The analysis of comonomer variations along the molar mass distribution in polyolefin copolymers is discussed. Selected applications of the method to polyethylene and poly(propylene) copolymers are presented.